The overall objectives of the project are: 1) to study the distribution of the epsilon-(gamma-glutamyl)lysyl isopeptide bond in cellular proteins and determine whether its frequency is modulated during mechanochemical processes like muscle contraction and protoplasmic streaming; 2) to determine whether the formation of a covalent inter- or intra-peptide chain bond can be detected directly by studying the chain content of contracting myofibrils; 3) to determine whether a specific cleavage enzyme mechanism for epsilon-(gamma-glutamyl)lysyl bonds is present in myofibrils or other systems. These objectives are part of an effort to test a theory of muscle contraction which proposes a Mg ions-activated formation of a phosphorylated intermediate and a Ca ions-activated covalent crosslinking reaction.